1. Field of the Invention
The present disclosure relates to an air shut-off valve apparatus for a fuel cell system. More particularly, the present disclosure relates to an air shut-off valve apparatus for a fuel cell system with which an air passage connected to a cathode of a fuel cell stack can be completely closed upon the halt of operation of a fuel cell system.
2. Description of the Related Art
A fuel cell system is a system for converting the chemical energy from hydrogen fuel and oxygen in the air into electricity through a chemical reaction, with the concomitant production of water. A fuel cell vehicle is a type of vehicle that uses the electricity from a fuel cell system to power its on-board electric motor.
Typically, a fuel cell system comprises a fuel cell stack, which generates electric energy and consists of a cathode (air electrode, oxygen electrode, reduction electrode) to which air is supplied, an anode (fuel electrode, hydrogen electrode, oxidation electrode) to which hydrogen is supplied, and an electrolyte membrane between the cathode and the anode.
After being drawn into a fuel cell system that is running, external air is humidified as it passes through a filter, a blower, and a membrane humidifier. The humidified air is then supplied to a cathode of the fuel cell stack.
Meanwhile, the hydrogen supplied to an anode of the fuel cell stack is dissociated into protons (H+) and electrons (e−) by a catalyst. Only the protons move through the electrolyte membrane to the cathode, while the electrons are drawn from the anode to the cathode through a gas diffusion layer and a separator plate, which are both conductive.
On the cathode, the protons and the electrons, which are supplied through the electrolyte membrane and the separator plate, respectively, react together with oxygen in the air to produce water, with the resultant generation of electricity owing to the flow of the electrons through an external circuit as the protons migrate.
When a fuel cell system is operated, therefore, the air that is humidified through a membrane humidifier is supplied to a cathode of a fuel cell stack, whereas the intake of humid air into the cathode should be blocked when the operation of the fuel cell system is halted. To this end, an air shut-off valve apparatus for controlling air intake is installed on the cathode side of the fuel cell stack.
In order to guarantee the durability of the fuel cell stack, an air shut-off valve apparatus, which is typically installed on each of the inlet and outlet sides of an air passage that communicates with the cathode, should completely block the inflow of humid air into the cathode upon the halt of the fuel cell system.
If the shut-off valve incompletely blocks the air passage communicating with the cathode when the fuel cell system is halted, humidified air continues to be introduced into the cathode, causing the corrosion and oxidation of a carbon support of the catalyst. As a result, the fuel cell stack deteriorates more rapidly, and thus decreases in durability.
In particular, the introduction of humid air into the cathode while the fuel cell system is halted may increase the circuit voltages of individual cells to such an extent as to damage the fuel cell stack, thus requiring that the start-up COD (cathode oxygen depletion), which is adapted to consume the increased voltage of individual cells upon start-up, be provided with increased capacity.
Moreover, such incomplete closure may lead to the introduction of foreign matter through the gap between the valve and the air passage.
The matters described as the background arts are only intended to increase the understanding of the background of the present invention, but should not be recognized as being prior arts which are already known to those skilled in the art.